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Community and Q&A

Problems with New Heat Pumps

jaltman | Posted in General Questions on

Hi there! We had a heat pump system installed in my photography studio last week and it has not performed as expected. There seem to be too many variables for me to pinpoint what the issue is but hopefully those more knowledgeable than I can help.

The space: 1400 sq ft, 35’x40′ wide open room with 10′ ceilings and an insulated concrete floor

The system: Mitusbishi Hyper Heat 28,600 BTU outdoor unit with two 15k BTU heads on opposite walls with MKH2 thermostats

The problem: This system cannot seem to keep the space above 55 or so when the temperature is at or below 15-20 degrees outside with setpoints at 70 degrees. The space will lose heat when the temperature drops and the heads are not even always running to try and gain ground. I have tried with the MKH2’s set to auto fan and manual fan and I have tried controlling from the remotes. At times the outdoor unit is not even running the fan, although I hear compressor like noises coming from it (outside of the 10 minute defrost cycles)

One other piece of information is that a couple days after install when it was clear the system was not performing properly, our contractor called his distributor and was instruction to flip a dip switch in the outdoor unit to increase the coil temperature(?) I can’t recall if that was the exact term.

I’m at a loss as to my next steps. I’m a little disappointed with my contractor as he seems to want to place blame on everything but the system, but it just doesn’t seem like it’s running as it should. I’d like to have a few ideas on how to troubleshoot it before I call my contractor back to come over.

Thank you!

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Replies

  1. PBP1 | | #1

    Seems odd. I have a Mitusbishi Hyper Heat 28,600 BTU outdoor unit (zone 5) with three heads (ducted) 15k, 12k and 9k (MHK1 thermostats), no problems for 2100+sqft, last night 7 F and 68 F indoors (set point). Can you provide R values ceiling/wall, window info and line lengths? Is one line long and the other short? Are both lines in conditioned space? Maybe a sketch of where the outdoor unit is with respect to heads?

  2. jaltman | | #2

    I'm glad to hear the sizing seems potentially correct. I don't have all of this information at hand but can see if I can find out. A crude sketch is attached though.

    The room has 3 large (8ft) double-hung double pane windows on the east wall and 2 5ft double-hung double pane windows on the south wall as well as a set of exterior french doors. No windows on the N or W walls.

    It is a trussed roof and there is about a foot of fiberglass batts on top of the ceiling joists. I was told by the people who built it there is 6" of fiberglass batts in the walls + 1" of foil faced insulation.

    In terms of the lines, one is quite short, maybe 10 feet and the other is around 50-60 feet. The unit with the short line seems to run more often than the other when the MKH2's are set to "auto fan." Neither of the lines are in a conditioned space, the short one is on the exterior of the building and the long one runs on top of the insulation in the attic.

  3. jaltman | | #3

    As of right now, the temperature outside is 6 degrees. The outdoor unit is not spinning. The head closest to the outdoor unit is not blowing air but is making some sort of noise. The head farthest from the outdoor unit is not doing anything.

    Setpoint is 70 on both MKH2 thermostats. One is reading 52 and the other 56.

    This hyper heat system should be producing heat at 6 degrees, right? Even if we do not have the most tightly sealed or insulated space? It almost feels like our system is not in hyper heat mode, even though I have been told that is not a thing.

    1. Cldlhd | | #46

      Yeah it seems very odd , I have Mitsubishi hyperheat, my house is only a little over 1000 sq ft and when it gets that cold I bump the temp up a degree or two but it works fine. There's definitely something wrong

  4. Expert Member
    Akos | | #4

    95% chance you have a leak and low refrigerant in your system.

    You can quickly check if you crank the thermostat up to max with the blower on high. Using a digital meat thermometer, measure the air temperature going into the head and coming out. You should see around a 30F delta, so in case of a 55F room, that should be around 85F air coming out of the unit. If you are not seeing this, there is a leak.

    Hyperheat is a type of compressor and refrigerant plumbing, the unit will always be running in hyper heat mode. There is no reason why you should not get full power out of your unit at 6F.

    We had spell of -4F here and had no problems with another brand of hyper heat unit.

    1. Kevin J | | #16

      We had multiple leaks at the fittings in our first year or two from a poor installation. It takes only a couple minutes for a tech to check the pressure with all units at max heat.

      Proper charge is critical, tolerance is very tight, especially with the long lineset run.

  5. jaltman | | #5

    That's a helpful metric, thanks!

    Both heads are measuring 66 going in and 86 coming out, so only 20F delta.

  6. tech1234 | | #6

    I have installed 10 or so hyper heats in various buildings. This sounds like something is wrong with the unit or the install. It can be hard to find a knowledgeable installer. Try to track down the "best in your area"

  7. PBP1 | | #7

    Try the temp rise test for each head, turn off one head and see temp rise and then turn off other head and see temp rise. The long run head may have losses and may be addressed by more insulation on long line. For example, the long run and return may be driving losses. It’s a two way street for refrigerant on the long run, losses coming and going. But you have experts responding with good info too.

    1. Deleted | | #8

      Deleted

  8. jaltman | | #9

    Thanks for the single head test idea. I isolated each head and gave it a few minutes to get going.

    Single head farthest from the outdoor unit: 73 in/ 116 out
    Single head close to the outdoor unit: 75 in/ 105 out

    This is really helpful in arming me with good information to approach my contractor. Would I be asking him for a refrigerant level check or a leak test?

    Also, do I want that dip switch returned to factory settings? The one that increases temperature at the coil?

    We have been using a lot more electricity than I anticipated with these running, which I am hopeful is indicative of them not running properly rather than what is to be expected. Especially considering they have not really been able to get up to temp and maintain it.

  9. jaltman | | #10

    Thanks to all who have helped. I shared this information with my contractor and he doesn't seem inclined to check refrigerant levels. He wants to explore replacing my system with a larger sized 36k system with a branch box, or an LP heater add on.

    It sure seems like something is not working properly if it's not even trying to heat the space sometimes rather than trying constantly and not succeeding.

    Any other advice?

    Thank you so much

    1. James Someone | | #12

      You didn't mention geographically where you are located.

      It sounds like you have a fair amount of glass in your 1400 sq ft studio. This may be contributing to a cold building. You also mentioned a French door, they tend to have poor air sealing at the weatherstripping, especially is they are builder grade quality. Air leaks will chill any building regardless of heat source.

      Twelve inches of fiberglass insulation in an attic is inadequate in most zip codes, this must be part of your problem also. You mentioned (6 inch of insulation) for walls but should clarify about the foil faced insulation. Is it applied to the exterior of the building or between the stud bays, the latter is a bit unconventional. Also under slab insulation, can you clarify the R value?

      My guess is you may have significant air loss thru the building and it is poorly insulated. It seems everyone is offering good advice but with out mention of more basic problem solving applied first.

      1. jaltman | | #17

        Hi James, thanks! We live in southern Vermont.

        Point taken. I would like to improve the insulation and air sealing in that space. I do not know the R value under the slab as we've only been here for 5 years and the previous owners were not able to dig that info up. I also do not know where exactly the foil faced insulation was installed.

        Let's assume air sealing and insulation could be better, I would still think that our system would be able to generate more heat at the heads when the outdoor temperature is colder.

        I am 10 days out from installation, if there is an issue with the system I'd like to address it ASAP while still within the install period.

        I can certainly look into better insulation and sealing but it probably won't happen until next winter with everyone so booked out.

    2. Josh Durston | | #13

      Can the contractor provide commissioning data (amp draws, temperatures in and out, refrigerant pressures, etc?). Commercially I work for a mechanical, and we have to provide this on every startup. If it gets missed, some returns to site and gets the startup documentation filled out.

      I would ask to pull the charge out and weigh it out and back in. Even if you have to pay, but make sure it's good meticulous service guy doing it.
      It impossible to know the charge without weighing it on these systems. If the charge is off, it may have no symptoms under some conditions and barely perform in other conditions.
      I would ask to check for leaks around the fittings and coils.

      There are clear formula's for the charge weight based on lineset length.
      Honestly pulling and recharging the system should take a couple hours max. Even you pay yourself it should only be a couple hundred dollars.

      Another thing to do that's one step beyond the delta t measurement. Is to look up the submittal data from the engineering guide and compare temp deltas and power/amps/watts.
      If it's low and charge it will likely have a lower peak power draw, but the capacity and efficiency may be greatly diminished under higher loads so it will just run and run. Draining your wallet but not giving much heat.

      https://mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10006\M-Series_Technical%20Data%20Book_01-2021.pdf

      documentation:
      https://mylinkdrive.com/USA/M_Series
      See how your equipment stacks up to the submittal data.

      1. jaltman | | #18

        Hi Josh,

        This is helpful, thank you. I can ask if he has commissioning data, my guess is no.

        I feel like I'm walking a fine line with him as almost immediately when things weren't working he backpedaled and tried to shift the responsibility on me for the size of the system installed saying it was what I wanted, not necessarily what he recommended. On the upside, it was good to see his true colors and that he isn't eager to accept responsibility.

        In terms of the charge and weight, is there something to be concerned about with doing this in cold temperatures? I thought I've read things about trouble with this stuff at or below 40 degrees.

        I think I would need to ask another contractor to come out to double check this guy's work rather than having him check his own work. Thank you for these links, it is so helpful for me to learn more about this so I can be less of a rube when dealing with him.

        I'm so pissed that I felt like he really knew his stuff, and maybe he does, but it's looking less likely.

        It seems exactly like what you said, it just runs and runs and is definitely draining our wallet but not heating the space. When the outdoor temperature is above 15 or so, it seems to keep the space at 68 with ease with the auto fan setting usually just running on low.

    3. Doug White | | #31

      WTH? He won’t check refrigerant levels wants sell you more equipment I hard to say it but all indications this is a poor contractor . Don’t be too hard on yourself we’ve all been taken at least once

  10. Andy CD Zone 5 - NW Ohio | | #11

    Jaltman, your contractor's response is absurd. That he won't do a basic check of the most likely culprit here (low charge) and instead is suggesting system replacement or LP supplement reveals that he's a charlatan.

    One final check on your part would be an air-leakage test of the structure. Is it possible that even with reasonable levels of insulation, you might have some massive air leaks? If you can confirm your building is reasonably tight, that bolslters the argument that the installation is bad.

    Was the installer connencted with the Mitsubishi Diamond program? Even if not, maybe a call to Mitsubishi customer service might bring some action.

    I have always wondered at the logic circuits of minisplits--they always seem to be executing strangely timed and mysterious processes--but if they can't eventually achieve at least an approximation of your setpoint, then they need repair. (Assuming of course that the design is appropriate.)

    1. Kevin J | | #15

      My Fujitsu units when in Auto fan mode, won't kick in to high fan unless it's 5 degrees below the set point. That logic is quite flawed.

    2. jaltman | | #19

      Thanks Andy.

      I think so as well. His first response when things weren't going right was to imply that my choice of this system (from options he provided) was the problem. He seemed a little too eager to shirk responsibility before even diagnosing. He has also suggested it is due to insulation, windows, even the concrete slab taking over a week to 'come to temp.' He hasn't totally checked out, but his suggestion of swapping out a larger system or adding an LP heater just doesn't seem to be addressing the issue.

      Even if the building had massive air leaks, wouldn't the system at least try to keep up? It does run a lot sometimes but doesn't produce much heat. Other times it seems it has given up (I am aware of the defrost cycles).

      My installer is diamond certified. I called Mitsubishi customer service but they couldn't give me much info beyond saying it didn't seem like the system was running right and that it did seem adequately sized.

  11. Expert Member
    Akos | | #14

    Can you check that actual part# on your outdoor unit?

    1. jaltman | | #20

      That was my thought. I was convinced I had the n0n-hyperheat model, but the sticker from Mitsubishi checks out on the outdoor unit

  12. Richard Levinson | | #21

    How are you measuring the room temperature? The reason I ask is, because I'm having trouble reconciling the temperatures you mention in posts #3 and #5. In post #3, the thermostats were reading 52º and 56º, but then an hour later you measured the return air temperature at 66º. That would suggest that the temperature at the heads was close to the setpoint.

    An then in post #9 you measured return air temps of 73º and 75º, which would suggest they're easily capable of getting the room (or at least the part where they're located) up to temperature.

    Is it possible that for some reason (i.e. uneven temperatures in the building due to lots of glazing or air leaks) the heads think the room is up to temperature when it actually isn't? Often minisplits default to using the return air temperature to determine room temperature, which might present itself as the issues you're seeing. Most will have settings to allow you to use the actual remote as the thermostat, which might help things.

    1. Expert Member
      Akos | | #22

      I think you are definitely onto something. The default setting on the units is to use the temperature sensor on the unit not on the remote. You have to go into the installer options on the remote and change it (the details to do this will take some digging).

      For the OP.

      I'm heating a 450sqft garage conversion (well sealed, 2x6 walls with batts, 2.5" rigid on the roof) with a budget non-hyper heat 12000BTU mini split. This looses bout 1/2 its capacity at 5F and I had no issues keeping the place at 68F during the last cold spell. So provided the place is somewhat air sealed and built to code min, the 28000BTU hyper heat should have absolutely zero issues keeping 1400sqft warm.

      1. PBP1 | | #26

        Agreed, the behavior of the setup seems odd given my almost 4 years experience in Montana with a 28.6k hyper-heat. Also, I would have expected the lower supply temperature to be at the head furthest from the ASHP.

        1. jaltman | | #27

          Hmm, I am not sure how to check on where it is sensing temperature. The units are being controlled by the MKH2 thermostats on opposite walls. At least that is how it appears. Any idea how I would double check that it is reading the room temp at the thermostat and not at the head? The Mitsubishi remotes cannot detect temp, only the heads and the MKH thermostats

  13. Jay Thomas | | #23

    A relatively easy non-invasive way to check for a leak is to check the input and output temperature from the unit with a thermal camera. You can check it at the air handler, then at the input and output of the compressor.

    You should see air coming out well above 100 deg F, and output fluid from the compressor above 100 F as well.

    It's almost certainly a leak - probably during installation - I had the same issue last year - performing much better with a recharge.

    Make sure you document whatever you do and use a HVAC professional at this point. The contractor is probably playing defense as once you have a leak best practice is to remove and replace all your refrigerant. And if they can't figure out why it leaked they are on the hook to replace all of the equipment.

    1. jaltman | | #28

      Hi Jay, would you be able to explain a little bit more on how to do this? Are these the copper pipes coming off the outdoor unit? I do not have a thermal camera however. I do have an infrared thermometer, would that work?

      1. Jay Thomas | | #41

        Yes - the copper pipes - and the aluminum fins inside. You could use a IR thermometer but it will be tough to get right. If you borrow an IR camera you can also look for air leaks.

  14. Jonathan Blaney | | #24

    I think you may have a problem with heat stratification. Cold concrete floors and warm ceilings. The heads are in the warm zone and the thermostats and people not. You are heating the top of the space. The floor is sucking up the warmth at the lower level. You may have enough BTUs to cover your heat loss but not enough to get that slab warm. Those wall heads may be putting the heat in the wrong place. How much attic insulation is there. Perhaps the wrong kind of heating system for that space.

    1. jaltman | | #29

      There is 12" of fiberglass batting in the attic.

      Would rugs help with the slab or is there any other solution other than putting in an insulated sub-floor and flooring?

      It is a world of difference when the outdoor temperature is above 15 degrees. The room stays at 65 pretty easily. With the fans on auto, they are rarely blowing at anything above 'low' and the room stays warm. Below 15 degrees and we just can't seem to hold any temperature in there and they don't seem to try very hard to do so.

  15. PBP1 | | #25

    If the 28.6k can't handle it when operating properly, I'd say insulate/air seal. The so-called 36k I believe is actually rated at about 42k, you don't want to be back on the boards here with a post about how much electricity is being used (unless you have it all taken care of with solar).

    Again, I have 2100+sq ft with three zones, one zone being completely isolated (separate entrance of space largely above garage) and my 28.6k hyper-heat handles it all even at sub-zero. Insulation/air sealing is cheap compared to the potential for huge electric bills. With an average monthly temp of 21 F (a couple sub-zero nights) and 1400+ Heating Degree Days (65 F), the heat pump uses just under 50 kwh per day or about 1500 kWh for the month, which is around $160 (about 0.11/kWh). A "36k" with 42k capacity/rating with multiple heads can only turn down to around 15k, which means it is possible that you'll be paying more any time the unit is on (demand for heat).

    I think I would press hard on the performance of the current 28.6k unit and insulation/air sealing.

    As to stratification, could be some part of the issue (cool floors) but I have elevated floors (on piers) with 9 ft to 13.5 ft sloped ceilings in a 24ft x 30ft (720 sq ft) great room (one of 3 zones) where the air handler/supplies can generate sufficient throw to break up the stratification. That great room also has 5 sliders and clerestory windows and no continuous exterior insulation such that the headers drastically reduce overall R value for the walls, not to mention 5 26ft long exposed 6x12 beams that run to the exterior (i.e., massive thermal bridges). Another zone is about the same size with 8ft to 11.5ft ceilings, exposed beams and plenty of glass. I found air sealing to work wonders (just be sure to monitor CO2 and other air quality indicators). Wishing you the best and if you get an explanation, please share if you can.

    1. jaltman | | #30

      Best case scenario would be that the system is the right system and it's running like a dream and all we need to do is focus on air sealing and better insulation.

      It just doesn't seem right that at 15 degrees the system can't hold a temperature in the space and it doesn't seem to try really hard to do so.

      We are using a lot of electricity, at least a lot more than I anticipated. We used to use right around 40kWh each day for two homes (my Dad is next door and on our meter) and now we are using over 100kWh each day.

      I just don't get the behavior in the cold temps. Would a space with bad insulation/air sealing cause the system to just give up? I would think it would be blowing as hard as it can, defrosting, and then continuing. Instead it just seems like it's not generating that much heat at the heads when it's below 15 degrees out.

      1. Doug White | | #32

        Bottom line as we’ve all learned the hard way there is no substitute for quality installer, equipment is agnostic. If anything mini splits double down on this mantra. Yet it is sooo hard to find this quality . A bit sad to realize Mitsubishi’s like other brands aren’t vetting their diamond guys better . When you feel you’ve exhausted your potential to get this guy to correct call another better dealer to check refrigerant if they correct send bill to original installer if he doesn’t pay , show your teeth don’t be a another victim go directly to bbb Yelp and state consumer agency to complain helll…take him to small claims court he won’t even show up to defend this nonsense.

        1. jaltman | | #34

          Thanks Doug. He is active on social media and has BBB stickers on his truck, I know his reputation is important. I have bit my tongue and stayed amicable so far but am definitely prepared to push hard when I know what it is I need from him. At this point, I prefer to have him on my side than not, at least until I better understand what I need done.

          I'm starting to get confused as to what I need. In my gut, the system isn't working right. I also have come to realize that the air sealing and insulation in the space needs to be upgraded. I don't think the two are related.

          If I am asking for a refrigerant leak/check, do I need to wait until the outdoor temperature is above 40 degrees? I am unclear on this.

          Is a refrigerant/leak check what I should be asking for? I don't think I want to explore replacing it with a larger 36k system or adding an LP heater right now as I am not convinced yet that it is undersized and that the only solution is a larger unit.

      2. K T | | #35

        Load and sizing could be a legitimate concern, assuming it's properly installed, charged and working as intended. The balance point for your space may simply be higher than 10-15 degrees even with a hyper heat system designed to work below that (Do heat strips kick in? I'm unfamiliar with the hyperheat units). The BTUs from the unit at those temps on the COP curve may simply be less than the Manual J or real world load of your space at those temps so it cant keep up without heat strips. Upsizing the unit increases the height (where vertical axis is BTU output) of the curve. Increasing air sealing/insulation doesn't change the curve but moves the balance point lower. Upsizing doesn't necc. mean you'd be using more energy overall as the variable speed would throttle down the kwh as outdoor temps rise.

        I think the problem with comparing everyone else's real world experiences is that it's anecdotal and everyone else's air sealing, windows, insulation and ultimately load is different. Someone may say they've got large space, colder temps, same unit and everythings fine but it's still apples to oranges. You'd need a good Manual J or other estimate to compare apples to apples.

        1. jaltman | | #37

          This makes sense to me, thank you. At that 15 degree inflection point, the building heat loss overpowers the system?

          I don't think this system has heat strips, just a pan heater to keep the outdoor unit warm?

          I'm working on the Manual J!

          1. K T | | #39

            Right, so the "balance point" is where the BTUs of the HVAC equal the BTU load of the space. Above that point the HVAC is providing more heat or cooling than is lost by the space. Below that the HVAC is not keeping up.

            Every HVAC and every space is different so what you usually get is a COP curve from the mfg that shows the BTUs of the HVAC. Then you compare that to the Manual J.

            Attached is a sample from the Carrier heat pump line. Decent heat pumps, but not as powerful at heating as your Mitsu unit is. Just shows you how it works.

            Each line is a different size rated unit (unit BTU ratings are for cooling I believe).
            You find an outdoor temp, say 15 degrees, and go up and see how much heat the 24K vs 36K unit puts out. Then you compare that to how much load your space has at that temp. Balance point would be where a diagonal line (the space load, as it varies w/ temp) crosses the COP curve.

  16. jaltman | | #36

    Got this back from the contractor today. Fancy sounding numbers but it doesn't mean much to me. Does this seem like a solid procedure?

    ""As far as the equipment goes, I will get myself and/or my guys to come do pressure tests. But it seems from what you said to be turning fans off and on inside and out as it should. It will turn off the fans to allow coils to pre-heat/pre-cool. The system was pumped down to below 500 micron, purged with nitrogen, vacuumed down again to below 500 micron, and factory charge released. The lines outside got hot to the touch after the usual 10-15min as we usually see. At that time, we were getting somewhat low delta T between supply and return. But, we were also dealing with pretty low ambient temps inside and outside the buildings envelope."

    1. PBP1 | | #38

      Thanks for posting info. Right now, it's 0 F outside and my Mitsubishi 28.6k unit has the house at 68 F (2100+ sq ft) with three ducted units (ducted performance is worse than that of a wall mounted head). Air sealing makes a difference. Why replace when some quick air sealing might solve the problem (if that's indeed the problem)?

      Oranges to apples, based on info, your Manual J is likely to be 50k+ which is incredibly high for your climate zone.

      If leakage is the issue, one big hole can make a huge difference. Maybe get a blower door test with a thermal camera and see where the losses are? You may have one or two bad spots?

    2. Mike Ferro | | #44

      The charging procedure mentioned of pumping the system down to 500 microns, breaking the vacuum with nitrogen, and then pumping it down again below 500 microns is appropriate to both check for leaks as well as eliminate any condensables that may be in the pipes prior to releasing the refrigerant.

      The one thing that's a bit strange is given your long line length to one of the heads I would have expected the contractor to have had to add additional refrigerant to supplement the factory charge. If additional refrigerant was required and he didn't add it, that would make a difference on heating/cooling performance although likely wouldn't cause the unit to shutdown.

      It's unclear what your contractor means by a "pressure test" but if that means he's going to put gauges on the system it won't tell him (or you) much. The only way to know if a heat pump system is properly charged is to weigh the refrigerant into the system. Or, in this case to remove the refrigerant and weight it in again.

      I'll note, I'm not a contractor, but hold an EPA refrigeration cert. So take my two cents with a grain of salt!

  17. Andy Kosick | | #40

    Few things:

    1 kWH per ton per hour below 20F is a good rule of thumb even for good cold climate minis. My MXZ-2c20nahz uses 40 to 50 kWh a day down there, so 50 to 60 is likely for yours

    It does seem like a reputable contractor should be willing the to come double check the system.

    An accurate Manual J really needs a blower door test, otherwise it can vary a lot.

    With stratification, 10’ ceilings, and high wall units, make sure you’ve tried running the fans on High and angle the louvers about 45 degrees to throw the air as far as possible and mix in the room. Believe it or not at low temps this might actually increase efficiency, especially if it reduces short cycling.

    If the unit is working right, I would try and bring the load of the building down to meet the system. You’ll be more comfy in the end.

    Good luck.

  18. Norman Farwell | | #42

    If the building has any serious performance issues (tongue and groove on the ceiling or no subslab insulation for ex) that unit could well be undersized.

    However if it’s functioning properly the indoor units should be blowing when there’s a call for heat and they are not in defrost.

    If you haven’t already, I’d try cycling the power to the unit. Leave it off for 10 minutes and then let it reboot. In my experience that resolves 95% things not related to refrigerant.

    If the fan shuts off while there’s a call for heat, that should have a fault indication on the LEDs on the odu. There’s no specific indication for low refrigerant, unfortunately, but it should indicate why it has shut fans off.

    1. James Howison | | #45

      Taking videos of any "codes" of the flashing LEDs on the inside and outside units is really helpful, especially if there are transient things. For the outdoor unit that means taking the cover off, unfortunately.

      Even leaving everything alone sometimes these reset by the time the contractor gets there (which is it's own sort of insanity for a unit that is easily capable of having a tiny screen and a log that can be scrolled back through ... of course a network connection to the contractor is another option but lots can go wrong with that too).

      The possibility that the units are using the internal temp sensors and call/satisfied cycles at different heads means that temp can go all over the place. You know, just another thing that would be obvious if these units had any sort of logging! How hard would it be to record sensed temp, calls (including 'clicks' on the VRF boxes), fans? Should also record watts used over time.

      Perhaps the Wifi/bluetooth control units will help be sure which temp sensing is being used (my Mitsu heads don't use the remote as a sensor, but these KumoCloud units were useful: https://www.ecomfort.com/Mitsubishi-PAC-USWHS003-TH-1/p81573.html I think they also require the WiFi module at each head: https://www.ecomfort.com/Mitsubishi-PAC-USWHS002-WF-2/p102719.html

      Note that the price and delivery times through the HVAC distributor were over double than online. The KumoCloud software is, well, it's ok, as far as these things go.

  19. Keith Gustafson | | #43

    I would think when the units are below setpoint they would run nonstop except when defrosting if they were trying

    Try forcing the fans on high

    Is it possible they are interfering with each other?
    Minisplit fans throw air really well, so if they are aimed at all toward each other...

    Are you turning them off/setting them back at night?
    I have noticed my theoretically oversized unit in my garage is not real good at recovery

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